The increasing interest in nano-scale and quantum devices has led to a correspondingly increased interest in capacitance measurement techniques suitable for such devices. Bridge circuits are often employed for capacitance measurements. If a bridge circuit is connected to a device under test (DUT) with conventional cables, the parasitic capacitance of the cables can overwhelm the capacitance of the device under test if the DUT capacitance is very low, as it often is for nano-scale devices.
An article by Ashoori et al. (Phys. Rev. Lett. v68n20 pp. 3088-3091 1992) describes the integration of a capacitance bridge circuit with the device under test, thereby avoiding the above indicated problem with conventional approaches. In this work, the bridge is tuned to a circuit operating point known as the balance point by adjusting the AC voltage amplitude on a standard capacitor that is part of the bridge circuit, and then measurements are performed. This work was performed at a cryogenic temperature (pumped 3He, giving a temperature of <1 K).
It is often desirable to perform sensitive capacitance measurements at more practical temperatures, such as 77K, or more preferably room temperature (i.e., ˜300K). Accordingly, it would be an advance in the art to provide high-resolution capacitance measurement techniques suitable for use over a broad temperature range.